When it comes to the last presidential election, the past is still not over. That much is clear in “American Chaos,” a documentary whose maker caught a whiff of Donald J. Trump’s early momentum and set out to interview some of his supporters in the months before Nov. 8, 2016.

That filmmaker, James D. Stern, was perplexed by a growing number of people backing Mr. Trump. Camera in hand, he spoke with Cuban immigrants in Florida, coal miners in West Virginia, a rancher in Arizona and others, at least one of whom said he twice voted for Barack Obama. Mr. Stern attended the Republican National Convention, and returned to Florida for election night.

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A preview of the film.Published OnSept. 4, 2018

It was a prescient plan. Mr. Stern, a longtime Democrat, vowed to listen closely, and he seems to have kept his word. Though he doesn’t mask his expressions — usually astounded, though never mocking — he’s a genial interviewer, empathic, he says, even if he can’t be sympathetic.

Most frequently, his interviewees voice disdain for a system they feel isn’t working for them. If, like Mr. Stern, you can’t fathom voting as they did, it’s possible to at least understand some of their emotions. (Though perhaps not those people whom we hear denying the facts of climate change, or those whose hatred of Hillary Clinton veers toward the pathological.)

Ultimately, “American Chaos” does little more than recap what’s already been said over the past two years. Yet like “11/8/16,” another recent documentary about the election, it gives a voice to many who are routinely ignored. “Passion beats pragmatism,” Mr. Stern says, summing up what he sees on his travels. Indeed, the message here is the same for both sides, for elections to come: Those who harness that passion gain the power.